DFB1r5 Design Review Thread

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Badwolf
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Re: DFB1r5 Design Review Thread

Post by Badwolf »

exxos wrote: Mon Jan 17, 2022 3:17 pm So in this instance, I will forgive you if you do not want to add them ;)
@Badwolf bows with a flourish.

:lol:

One place I have added optional pull-ups is on the bus control lines.

Reset could just be a squiffy old cap, but I've found that benefits above about 45MHz from having some upward assistance. Some or all of BR, BG or BGK occasionally simply don't work if probed. Two of them are great big lines spanning all the various DMA bits and bobs and a little extra capacitance throws them off the deep end. I figured it would't hurt to have the option of a bit more of a pull on those.

BW
DFB1 Open source 50MHz 030 and TT-RAM accelerator for the Falcon
DSTB1 Open source 16Mhz 68k and AltRAM accelerator for the ST
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
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exxos
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Re: DFB1r5 Design Review Thread

Post by exxos »

Badwolf wrote: Mon Jan 17, 2022 3:36 pm Reset could just be a squiffy old cap, but I've found that benefits above about 45MHz from having some upward assistance. Some or all of BR, BG or BGK occasionally simply don't work if probed. Two of them are great big lines spanning all the various DMA bits and bobs and a little extra capacitance throws them off the deep end. I figured it would't hurt to have the option of a bit more of a pull on those.

The reset circuit pretty much the same as always. The two reset caps need replacing and upping in value and swapping about and I have been putting a 1K pullup on reset on my boosters for several years now as well.

If probing causes problems, then definitely at some pullups on them. A lot of people do not bother doing those tests and it will always bite them in the rear in the end.

I had similar with the 32MHz clock on my booster. it would run perfectly fine all day (even on multiple machines) but as soon as the scope probe is added (even on x10) the thing would become unstable. That to me is not "satisfactory" so I get fiddling until stable while also having the scope probe attached.

It is not like scope probe is really have that much capacitance to start with, but when you're dealing with MHz stuff.. That stuff seriously adds up. You could get a few pF difference between manufacturing tolerances on the PCB itself. I have run into that problem in the past as well. So literally going from one batch of boards to another is enough to break a otherwise working design.
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Badwolf
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Voltage Regulator Choice

Post by Badwolf »

I've always used LM1117s in my board for voltage regulation, but it turns out these are hard to come by at the moment.

Never mind! Lots of SOT-223 3.3V regulators. I'll just choose a different brand.

Ah...

Screenshot 2022-01-24 at 10.33.38.png
Screenshot 2022-01-24 at 10.33.38.png (11.54 KiB) Viewed 2137 times


Seems the right hand footprint is far more common (in available stock) than the left most (which is my LM1117 layout). I didn't spot this on my last order and have a bunch of the -HA footprint items in my grubby little mitt at the moment.

So the question is what (in our esteemed forum readers' opinions) is the footprint of choice for SOT-223 regulators?

I've not pressed the 'go' button on the DFB1r5 order yet as this is the sort of thing I probably ought to make a decision on. I *may* be able to rejig a few things and put both footprints on the board, but that could just get confusing and I reckon it's worth thinking about the long-term plan for other boards whilst I'm at it.

Any thoughts?

BW
DFB1 Open source 50MHz 030 and TT-RAM accelerator for the Falcon
DSTB1 Open source 16Mhz 68k and AltRAM accelerator for the ST
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
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Re: DFB1r5 Design Review Thread

Post by exxos »

That tripped me up on the H5 with one previous 3.3v reg as well :roll:

I guess it's what generally used and most available pinout which may be the deciding factor. But IMO I tend to go for tab is ground. Other pinouts mess with my head :stars:
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Re: DFB1r5 Design Review Thread

Post by Badwolf »

exxos wrote: Mon Jan 24, 2022 10:47 am That tripped me up on the H5 with one previous 3.3v reg as well :roll:

I guess it's what generally used and most available pinout which may be the deciding factor. But IMO I tend to go for tab is ground. Other pinouts mess with my head :stars:
I was toying with the idea of doing a combined footprint with four pads down the right hand side. Vin at each end. Isolated tab.

But if I were to ever go for SMD assembly I'm not sure quite how much that would f%*k things right up. :)

BW
DFB1 Open source 50MHz 030 and TT-RAM accelerator for the Falcon
DSTB1 Open source 16Mhz 68k and AltRAM accelerator for the ST
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
FrontBench The Frontier: Elite 2 intro as a benchmark
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Re: DFB1r5 Design Review Thread

Post by exxos »

K.I.S.S ;)
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https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Re: DFB1r5 Design Review Thread

Post by sporniket »

O.o ...

Well, without regards to time, pcb space, budget, motivation etc..., I would apply on hardware design what I do routinely for software when I write my own interface abstraction to accomodate several functionnal equivalent component with their own incompatible API : do a breakout module where I decide the layout, say :

Code: Select all

    +--+
VIN-|  |-VOUT
VIN-|  |-VOUT
GND-|  |-GND
GND-|  |-GND
    +--+
For versatility, the breakouts would be 0.1' pitched header pins, so that it can also used for breadboard.

Then you can have one version taylored for the chip available.

I understand this is supplemental work and may be out of question.
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Re: DFB1r5 Design Review Thread

Post by Badwolf »

sporniket wrote: Mon Jan 24, 2022 1:43 pm I understand this is supplemental work and may be out of question.
Yeah, having a whole separate board for the plug in with its own separate manufacturing process doesn't really work as well as a translation layer in software.
sporniket wrote: Mon Jan 24, 2022 1:43 pm For versatility, the breakouts would be 0.1' pitched header pins, so that it can also used for breadboard.
A pin pitch of a tenth of a foot, eh? How big do you reckon my voltage regulator is? :lol:

(I know what you meant, but we've all seen Spinal Tap ;) )

BW
DFB1 Open source 50MHz 030 and TT-RAM accelerator for the Falcon
DSTB1 Open source 16Mhz 68k and AltRAM accelerator for the ST
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
FrontBench The Frontier: Elite 2 intro as a benchmark
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Re: DFB1r5 Design Review Thread

Post by sporniket »

Badwolf wrote: Mon Jan 24, 2022 2:13 pm
sporniket wrote: Mon Jan 24, 2022 1:43 pm For versatility, the breakouts would be 0.1' pitched header pins, so that it can also used for breadboard.
A pin pitch of a tenth of a foot, eh? How big do you reckon my voltage regulator is? :lol:

(I know what you meant, but we've all seen Spinal Tap ;) )

BW
:lol:
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Re: DFB1r5 Design Review Thread

Post by Badwolf »

I think, after a bit of mulling over, I'm going to stick with my current fooprint (which is the traditional centre tab = Vout layout).

I think it reduces the possibility of captain cockup coming to town, although it does cause a bit of an issue at the moment with a lack of LM1117 and equivalent available.

JLCPLB do have some in stock, though, so when I do the order I might even have a dab at the SMD assembly business.

For the dev work I'm doing the hacky workaround for the inadvertant alternative-pinout stock I have is simple enough in the meantime.

BW
DFB1 Open source 50MHz 030 and TT-RAM accelerator for the Falcon
DSTB1 Open source 16Mhz 68k and AltRAM accelerator for the ST
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
FrontBench The Frontier: Elite 2 intro as a benchmark
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